3rd generation partnership project (3GPP) long term evolution (LTE) is an improved version of a universal mobile telecommunication system (UMTS) and is introduced as the 3GPP release 8. The 3GPP LTE uses orthogonal frequency division multiple access (OFDMA) in a downlink, and uses single carrier-frequency division multiple access (SC-FDMA) in an uplink. The 3GPP LTE employs multiple input multiple output (MIMO) having up to four antennas. In recent years, there is an ongoing discussion on 3GPP LTE-advanced (LTE-A) that is an evolution of the 3GPP LTE.
An LTE-A system employs new techniques such as carrier aggregation and a relay. The carrier aggregation is used to flexibly extend an available bandwidth. The relay is used to increase a cell coverage and support group mobility and to enable user-centered network deployment.
The relay provides two types of radio interfaces. One is a Uu interface between a relay and a user equipment, and the other is a Un interface between the relay and a base station. A radio bearer is set up in each radio interface. In order for the user equipment to receive a service from the base station via the relay, two radio bearers need to be set up.
Since a plurality of radio bearers are set up due to the introduction of the relay, the setting up of the radio bearers may be delayed. As a result, a service provided to a user equipment may be delayed. Therefore, there is a need for a method capable of effectively setting up the radio bearers.